According to the characteristics that the wave length of electromagnetic wave may be shortened when the electromagnetic wave travels in high dielectric constant substances, a traditional metal material can be replaced with a dielectric material; and under a same index, the volume of a filter may be decreased. The research for the dielectric filter is a hot point in the communication industry all the time. As an important component of a wireless communication product, the dielectric filter is very significant for the miniaturization of a communication product.
As shown in FIG. 1, generally, a TM mode dielectric resonator mainly includes a dielectric resonant column 103, a sealing cover plate 102, a tuning screw 101 and a metal cavity 104. The lower surface of the dielectric resonant column 103 is directly welded on the metal cavity 104 and is used for tightly contacting with the bottom surface of the metal cavity; and the sealing cover plate 102 is sealed with the metal cavity 104 through a screw to form a sealing cavity. When the dielectric resonator runs normally, high electric field is distributed at the joint part between the lower end surface of the dielectric resonant column 103 and the metal cavity 104. Because the dielectric resonant column is directly welded at the bottom of the metal cavity, when the lower end surface of the dielectric resonant column does not fully contact with the metal cavity, the impedance may become discontinuous, the field energy cannot be transmitted out, the high dielectric constant and high quality factor of the dielectric resonant column cannot be shown, and even media may be burnt up. Therefore, a very high requirement is set to the process of welding the dielectric resonant column with the metal cavity into a whole; in addition, the shedding phenomenon in the processing of welding the dielectric resonant column with the metal cavity may affect the performance and the service life of the dielectric resonator seriously. Therefore, whether the lower surface of the dielectric resonant column contacts with the surface of the metal cavity well in the TM mode dielectric resonator is very critical, and how to solve the problems of fixation and contact for the TM mode dielectric resonant column becomes a key research direction for the application of the dielectric resonator.
In a Chinese patent CN201020643211, a TM mode dielectric filter is described, which includes a metal resonant cavity, a cover plate, a tuning screw and a TM mode dielectric resonator, wherein the TM mode dielectric resonator is fixed inside the metal resonant cavity through a screw. The TM mode dielectric filter is characterized in that the screw rod part of the screw passes through a location hole of the TM mode dielectric resonator to be tightly screwed at the bottom or on a side wall of the metal resonant cavity; the screw rod part of the screw does not contact with the location hole; and a transition gasket is arranged between the head part of the screw and the location hole end surface of the TM mode dielectric resonator to separate them. The specific implementation process in the patent is complex in assembly process, and has a high requirement on the structure design and a great influence on the performance, so as to be unfavourable for batch production and cause a high production cost.